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Topic: (Newbie Qsn) Inverse Quantization (Read 955 times) previous topic - next topic

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  • ksr
  • [*]
(Newbie Qsn) Inverse Quantization
hi to all,

i am trying to implement mp3 decoder with the information in ISO/IEC 11172-3, from the last two weeks, and i successfully completed, frame fetching, side information decoding, scalefactors reading and huffman decoding... and now i am into inverse quantization......
here now i am not getting how to implement the iq as it is in the specifiaction

* here 576 frequency samples(for long blocks) decoded from huffman will be given input to inverse qunatizer, there we will process it as
  32 subbands and each subband of 18 samples (so totally 576 frequency samples ).
and here in "iq" i have the values of

                                                global_gain[gr]
                                                subblock_gain[window][gr]
                                                scalefac_s[gr][ch][sfb][window]
                                                scalefac_l[sfb][ch][gr]
                                                pretab[sfb]
                                                preflag[gr]

I am having all these values, which are computed at decoding sideinformation except "scalefac_multiplier".

here i have to get scalefactor band value (sfb), how i have to calculate here from the tables i have for 32k, 42.1k, 48k(as there are 22 values for long blocks).

here are my questions:
1) what is the value of scalefac_multiplier?
2) how to get the values of "sfb" and "widow" which values i have to use (as sfb index varies from 0 to 21 and window 0 to 2)